fix Issue 20855 - stack overflow when compiling large file

src/dmd/backend/backconfig.d

@@ -110,6 +110,8 @@ static if (TARGET_WINDOS)
     {
         config.exe = EX_WIN32;
         config.ehmethod = useExceptions ? EHmethod.EH_WIN32 : EHmethod.EH_NONE;
+        if (mscoff)
+            config.flags |= CFGnoebp;       // test suite fails without this
         config.objfmt = mscoff ? OBJ_MSCOFF : OBJ_OMF;
         if (mscoff)
             config.flags |= CFGnoebp;    // test suite fails without this

src/dmd/backend/blockopt.d

@@ -660,13 +660,19 @@ void blockopt(int iter)
             blexit();
             if (iter >= 2)
                 brmin();                // minimize branching
+            version (MARS)
+                // Switched to one block per Statement, do not undo it
+                enum merge = false;
+            else
+                enum merge = true;
+
             do
             {
                 compdfo();              /* compute depth first order (DFO) */
                 elimblks();             /* remove blocks not in DFO      */
                 assert(count < iterationLimit);
                 count++;
-            } while (mergeblks());      /* merge together blocks         */
+            } while (merge && mergeblks());      // merge together blocks
         } while (go.changes);
 
         debug if (debugw)

src/dmd/backend/cgcod.d

@@ -257,6 +257,8 @@ tryagain:
     mfuncreg = fregsaved;               // so we can see which are used
                                         // (bit is cleared each time
                                         //  we use one)
+    assert(!(needframe && mfuncreg & mBP)); // needframe needs mBP
+
     for (block* b = startblock; b; b = b.Bnext)
     {
         memset(&b.Bregcon,0,b.Bregcon.sizeof);       // Clear out values in registers
@@ -1016,7 +1018,6 @@ else
         // we need BP to reset the stack before return
         // otherwise the return address is lost
         needframe = 1;
-
     }
     else if (config.flags & CFGalwaysframe)
         needframe = 1;
@@ -1034,7 +1035,9 @@ else
                 anyiasm ||
                 Alloca.size
                )
+            {
                 needframe = 1;
+            }
         }
         if (refparam && (anyiasm || I16))
             needframe = 1;

src/dmd/backend/go.d

@@ -288,12 +288,13 @@ else
     // Each pass through the loop can reduce only one level of comma expression.
     // The infinite loop check needs to take this into account.
     // Add 100 just to give optimizer more rope to try to converge.
-    int iterationLimit = 0;
+    int iterationLimit = 100;
     for (block* b = startblock; b; b = b.Bnext)
     {
         if (!b.Belem)
             continue;
-        int d = el_countCommas(b.Belem) + 100;
+        ++iterationLimit;
+        int d = el_countCommas(b.Belem);
         if (d > iterationLimit)
             iterationLimit = d;
     }

src/dmd/backend/gother.d

@@ -1290,7 +1290,7 @@ private bool copyPropWalk(elem *n,vec_t IN)
         {
             Symbol *v = n.EV.Vsym;
 
-            //printf("Checking copyprop for '%s', ty=x%x\n",v.Sident,n.Ety);
+            //printf("Checking copyprop for '%s', ty=x%x\n", v.Sident.ptr,n.Ety);
             symbol_debug(v);
             const ty = n.Ety;
             uint sz = tysize(n.Ety);
@@ -1309,7 +1309,7 @@ private bool copyPropWalk(elem *n,vec_t IN)
                     csz = cast(uint)type_size(c.ET);
                 assert(cast(int)csz >= 0);
 
-                //printf("looking at: ("); WReqn(c); printf("), ty=x%x\n",c.EV.E1.Ety);
+                //printf("  looking at: ("); WReqn(c); printf("), ty=x%x\n",c.EV.E1.Ety);
                 /* Not only must symbol numbers match, but      */
                 /* offsets too (in case of arrays) and sizes    */
                 /* (in case of unions).                         */
@@ -1333,7 +1333,7 @@ private bool copyPropWalk(elem *n,vec_t IN)
             {
                 debug if (debugc)
                 {
-                    printf("Copyprop, from '%s'(%d) to '%s'(%d)\n",
+                    printf("Copyprop, '%s'(%d) replaced with '%s'(%d)\n",
                         (v.Sident[0]) ? cast(char *)v.Sident.ptr : "temp".ptr, cast(int) v.Ssymnum,
                         (f.Sident[0]) ? cast(char *)f.Sident.ptr : "temp".ptr, cast(int) f.Ssymnum);
                 }

src/dmd/backend/symbol.d

@@ -262,9 +262,17 @@ bool Symbol_isAffected(const ref Symbol s)
     if (s.Sflags & SFLunambig)
         return false;
 
-    /* If it's immutable, it can't be affected
+    /* If it's immutable, it can't be affected.
+     *
+     * Disable this check because:
+     * 1. Symbol_isAffected is not used by copyprop() and should be.
+     * 2. Non-@safe functions can temporarilly cast away immutable.
+     * 3. Need to add an @safe flag to funcsym_p to enable this.
+     * 4. Const can be mutated by a separate view.
+     * Address this in a separate PR.
      */
-    if (s.ty() & (mTYconst | mTYimmutable))
+    if (0 &&
+        s.ty() & (mTYconst | mTYimmutable))
     {
         return false;
     }

src/dmd/s2ir.d

@@ -764,6 +764,11 @@ private extern (C++) class S2irVisitor : Visitor
                 incUsage(irs, s.loc);
 
             block_appendexp(blx.curblock, toElemDtor(s.exp, irs));
+
+            // goto the next block
+            block* b = blx.curblock;
+            block_next(blx, BCgoto, null);
+            b.appendSucc(blx.curblock);
         }
     }
 

test/runnable/test20855.d

@@ -0,0 +1,26 @@
+// https://issues.dlang.org/show_bug.cgi?id=20855
+
+string exp()
+{
+    string s = "a = b + c * d + a;";
+    foreach (i; 0 .. 12)
+	s = s ~ s;
+    return s;
+}
+
+int test()
+{
+    auto a=1, b=2, c=3, d=4;
+    mixin(exp());
+    return a;
+}
+
+import core.stdc.stdio;
+
+int main()
+{
+    int a = test();
+    printf("a = %d\n", a);
+    assert(test() == 57345);
+    return 0;
+}